Putting on new cork and felt bumpers is
really a job for an experienced repairman, but in an emergency you may have
to do the job yourself. If regular cork bumpers are hot available, one can
be made from an ordinary bottle cork. Clickless valves, be sure to glue on
cork and felt with a glue not readily soluble in water, or saliva will soak them loose. Avoid getting any glue on the piston or casing walls,
and be sure the slot in the cork and felt is centered so the pin will move
up and down freely in this slot without touching.

Most valve stems are marked to indicate
just how high the bumper and felt should be to allow the piston to come up
so that the ports in the pistons accurately meet the knuckles in the casing.
If there is such a mark on the valve stem, it is easy to cut the cork so the
piston will stop at the proper place when the finger releases it. Keep
shaving or sanding off the cork until when you sight across the top of the
valve cap, the mark on the valve stem is level with the top of the valve
cap, then you know the cork and felt are the proper height.

If there is no such mark, you'd better
let an experienced repairman do the job. It is extremely important that the
height of cork and felt is correct, otherwise the ports in the piston and
the knuckles in the casing will not meet accurately, and the instrument will
blow stuffy and will lack resonance.